The literature on various forms of diagnostic test methods including specific binding assays, especially immunoassays, is extensive and commercial products are numerous. A large number of simplified and conveniently packaged assays are currently available. Nonetheless, there remains a need for assay devices which are easy to use and interpret.
Whole blood samples may obscure the reading of test results due to turbidity and color. In order to solve this problem, previous investigators have described devices which both separate out the Red Blood Cells (RBCs) and analyze the resultant plasma or serum for a particular dissolved component. EPO Publication No. 287731 to Maddox describes a dry test device comprising an absorbent reagent zone containing a chemical assay or immunoassay and an analyte target having a polysaccharide material that can limit the passage of RBCs or hold the RBCs on or near the surface of the absorbent reagent zone. A one-step procedure, employing simultaneous separation from whole blood with testing for a desired component is described in U.S. Pat. No. 4,678,757 to Rapkin et al. Blood is applied to the surface of a carbohydrate-treated carrier. The fluid portion migrates away from the point of contact and the cellular components remain in close proximity to the point of contact. If the carrier is further treated with a reagent employed to detect a component, a color will appear in the fluid. U.S. Pat. No. 3,552,928 to Fetter describes a means for separation of whole blood into a colorless fluid and a red cell or residue component. The whole blood is contacted with a separative reagent (a water-soluble, nonvolatile amino acid), the residue is removed and the remaining fluid can be contacted with a test reagent. Both reagents may be contained on a single matrix (i.e. bibulous filter paper), however, the matrix must allow the colorless fluid to flow from the separating reagent to the test reagent. U.S. Pat. No. 4,594,327 to Zuk describes a procedure whereby blood is first treated with a red blood cell precipitant, such as an antibody, lectin or certain polymeric amino acids, and then passed into an "immunochromatograph." The red blood cells remain at the liquid/air interface.
U.S. Pat. No. 4,943,522 to Eisinger et al. describes methods and apparatus for conducting specific binding pair assays, such as immunoassays. A porous membrane capable of non-bibulous lateral flow is used as assay substrate. A member of the binding pair is affixed in an indicator zone defined in the substrate. The sample is applied at a position distant from the indicator zone and permitted to flow laterally through the zone. Analyte in the sample is complexed by the affixed specific binding member and detected.
All patents, patent applications, and publications mentioned herein, whether supra or infra, are hereby incorporated by reference.